1. Field of the Invention
This invention relates to apparatus for separating the output of material grinders into fine material while returning coarse material that requires further reduction.
2. Description of the Prior Art
In the reduction of coarse material, like rock, coal and similar substances, the grinding apparatus has a tendency to discharge the product before it has been reduced to a uniform desired size. Heretofore the grinding apparatus has been provided with product separation means for the purpose of allowing the desired fines to pass on to the outlet while returning the coarse fractions for further reduction. In some instances the coarse returning fractions accumulate in a large enough mass to obstruct the fine discharge from the grinding apparatus. This latter situation is undesirable as the output is obstructed and the power to drive the apparatus is increased in order to be able to move the mass of material which has considerable density.
When the mass of material increases there is a lack of effective separation from two standpoints. One is that when the air flow is too high the larger particles are carried along with the fines and get into the conduit and drift along as an impedement to uniform flow. When the outlet conduit connects into a burner, the large particles reach the combustion zone and fail to burn completely. In the second case, the power to drive the rotating blade elements increases rapidly when the mass of material becomes dense, and greater horse power is required.